Transducer suspension system



Aug. 7, 1962 E. M. wElss TRANSDUCER SUSPENSION SYSTEM Filed April 17, 1961 INVEN'TORI igawfiiflfm,

ATTORNEYS.

United States Patent Ofiice 3,48,568 Patented Aug. 7, 1952 3,048,668 TRANSDUCER SUSPENSION SYSTEM Erwin M. Weiss, Chicago, llll., assignor to Beltone Hearing Aid Company, a corporation of Illinois Filed Apr. 17, 1961, Ser. No. 103,637 11 Claims. (Cl. 179-179) This invention relates generally to a mounting for a transducer and more particularly to a new and improved transducer mounting of the type having advantageous use in electro-acoustical devices, such as hearing aids and the like.

Those skilled in the transducer art know that the problem of mounting a transducer to reduce the adverse effects of mechanical feedback is one of the most serious and critical areas in the construction of electro -acoustical devices.

In the field of hearing aids, for example, wherein microphone and receiver transducers normally are mounted close to each other in a compact n'gid casing, vibration of the casing can be transmitted to a transducer with extremely disturbing results to the wearer.

As a result, many attempts have been made in the prior art to eliminate or attenuate the transmission of easing vibrations to the microphone and receiver transducers due to the normal use of the hearing aid and to sudden movements resulting from shock or impact of the transducer within the case. Such prior art attempts generally have taken the form of various resilient rings or sheets upon which the transducer is supportingly mounted in the casing, or resilient sheaths which enclose the transducer within the casing.

The transducer mounts of the prior art have not proved entirely satisfactory for a number of reasons. Normally, such mounts are made of foam or sheet rubber, which have high internal damping characteristics. Accordingly, any change in the rubber mount material, such as stiffening after a period of time, results in an undersirable change in the internal damping characterisics, Thus, such rubber mounts have been susceptible to the corrosion producing effects of ozone, the brittleness producing effects of light, and the elasticity producing efiects of heat, and it has been common for such prior art mounts to take a permanent set-all of which is in derogation of maintaining a constant, desired internal damping characteristic.

Accordingly, it is a general object of this invention to provide a new and improved transducer mounting means which overcomes the deficiencies of the prior art mounts.

It is another object of this invention to provide a new and improved transducer mounting means comprising a plurality of hollow tubular members disposed around the transducer for isolating the latter against mechanical feedback transmitted by the rigid casing and for insulating the transducer against shock resulting from the dropping of the casing or rapid movement thereof.

It is still another object of this invention to provide a new and improved transducer mounting means, as above, wherein the hollow tubular members suspending the transducer are formed of a relatively inert viscoelastic material whereby damping is provided by the combination of the internal damping characteristics of such material together with the air within the tubular members and is not solely a function of the visco-elastic material forming the tubular member.

It is a further object of this invention to provide a new and improved transducer mounting means, as described, comprising a plurality of hollow tubular members disposed around the transducer for mechanically isolating the latter from casing vibration wherein the isolation is provided by the compliance of the tubular members in combination with the damping effect of the moving air column within the tubular member.

It is a still further object of this invention to provide a new and improved transducer suspension formed of a plurality of hollow tubular members having non-linear compliance and non-linear damping characteristics for effective damping of large amplitude and low frequency vibrations which may arise from casing movement, shock and the like.

It is another object of this invention to provide a new and improved suspension system for a transducer comprised of a plurality of spaced, cylindrical hollow tubular members having a unique rolling action against the casing for reducing mechanical coupling of the transducer to the walls of the casing.

It is still another object of this invention to provide a new and improved transducer suspension system, as described, comprising one or more sheaths in the form of boots or bands shaped to fit over the transducer and having at least one hollow tubular member on each wall which serves to properly locate and seat the transducer and mount assembly in the casing cavity when the assembly is dropped into the cavity and thereby eliminates the need for skillful operators or special buffers for efficient assembly practices.

It is a still further object of this invention to provide a new and improved transducer mounting means as described which is characterized by its highly eflicient vibration isolation properties, its economies of manufacture and assembly, and its many other advantages over transducer mounts of the prior art.

The novel features which are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with the further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevational view of a portion of an eyeglasses hearing. aid temple member partly broken away to show a transducer and mount embodying the present invention;

FIGURE 2 is an exploded view of a transducer and mount assembly in accordance with the invention comprising a microphone and two sheaths formed as halfbooths each having a plurality of hollow tubular members disposed therearound;

FIGURE 3 is an end elevational View of a boot or band type of sheath showing the hollow tubular members as attached to the sheath at a tangential point of the tubular members to avoid deformation of the latter when the sheath is elongated; and

FIGURES 4 and 5 are cross-sectional views of a casing with a transducer mount operatively positioned therein illustrating the isolation action of a boot or band type of mount during two different degrees of movement of said transducer within the casing.

Referring now to the drawing, and more particularly to FIGURE 1 thereof, there is illustrated one particular embodiment of the invention as advantageously utilized in a temple member of hearing aid eyeglasses. While the invention is illustrated in connection with a hearing aid, it will readily be appreciated by those skilled in the art that the novel transducer mounting means may be utilized in many other types of electro-acoustical devices in addition to hearing aids Where mechanical vibratory isolation between the transducer and the case is an important factor.

As shown in FIGURE 1, a transducer such as a microphone is positioned in a casing cavity -12 defined by external and internal walls of the hearing aid casing 14. Thus, the longitudinal walls 16 and 18 of the casing together with the transverse walls 20 and 22 define a cavity shaped to receive the transducer and suspension assembly. The transducer suspension assembly in accordance with this illustrative embodiment of the present invention comprises a pair. of sheaths, in the form of boots 24, of relatively inert, visco-elastic material snugly fitted over the opposite ends of the transducer 10 and having a plurality of elongated tubular members spaced therearound for isolating the transducer 10 in the cavity '12 from the hearing aid casing 14 so as to attenuate the transmission mechanical vibratory feedback therefrom.

The details of the invention are better shown in the exploded view of FIGURE 2. It can there be seen that a microphone type of transducer 10 is adapted to be supported in the hearing aid casing cavity by the plurality of elongated open-ended, hollow, tubular members which are spaced around each wall of the boot 24 adapted to be in contact with the walls of the casing cavity 12. Thus, the transducer suspension sheath 24 is shaped to fit snugly in closely fitting relationship about the transducer 10 with each wall thereof having one or more hollow, tubular members 26 provided thereon. While the hollow, tubular members 25 are illustrated in cylindrical form in the drawing, it will be appreciated by those skilled in the art that the tubular members may have any other suitable configuration, as :for example, oval tubes, triangular tubes and rectangular tubes. Thus, the invention is not to be limited to the cylindrical tubes illustrated which is merely one preferred embodiment.

In accordance with a feature of this invention, the boot 24 and tubular members 26 are formed of a relatively inert, visco-elastic material which may have relatively little internal damping characteristics. In prior art transducer mounts, such as those formed of rubber, the mounts were required to have high internal damping, and the material for such mounts was chosen to provide this particular characteristic. One of the disadvantages of the prior art constructions was the tendency of such mounts to change in stiffness or take a permanent set with the adverse result that the internal damping characteristics of the mount would deteriorate with time.

In accordance with a feature of this invention, these undesirable results of prior art mounts have been eliminated since the damping function is provided by the moving air column within the tubular member in combination with the damping characteristics of the mount and is not a function of the mount material per se. It has been found that a moldable visco-elastic mterial, such as the silicone types manufactured by the Dow-Corning Company is quite satisfactory for this purpose due to its low internal damping characteristics, its relatively inert properties, and its resistance to the adverse effects of ozone, light and heat. However, it will be understood that other types of visco-elastic materials having good life characteristics with different internal damping characteristics also may be used for the fabrication of the unique transducer mount of the present invention since the total damping provided is the sum of the damping achieved by the air movement within the tubular materials together with the damping in the visco-elastic material itself. However, it will be understood that preferably the sheath interconnecting the tubular members be selected so that its internal damping characteristics normally plays no part in the isolation function of the mount.

It is highly desirable for electro-acoustic transducer mounts to have a very low resonant frequency characteristic. Advantageously, the resonant frequency range of such mounts should be well below the amplifier frequency range to avoid any unwanted modulation of audio or extraneous sounds. In addition, this characteristic is desirable to enhance the attenuation of the mechanical vibration transmitted to the transducer from the transducer casing. However, the resonant frequency of the transducer mount cannot be lowered below certain lower frequency limits without raising the possibility of additional problems.

In accordance with a feature of the present invention, the novel hollow tubular members of the mount have the desirable characteristics of low frequency resonance for small deflections, and an increasing resonant frequency for large deflections. Thus, the transducer suspension mount will not sustain large amplitude, low frequency vibrations and oscillations tend to die out quickly. Those skilled in the art will appreciate that this highly advantageous feature serves to avoid the prior art problems of lead breakage which may occur during shipment of the transducers, and from casing movement and shock.

These unique features are attained in the present inven tion due to the non-linear damping and non-linear compliance characteristics which are provided by the novel construction. The non-linear compliance characteristic of the present invention is such that as the pressure or deflection increases, the mount becomes stiffer. The nonlinear damping characteristic of the invention is such that for any given frequency, the damping increases as the amplitude of vibration increases. Accordingly, such nonlinear damping and non-linear compliance characteristics serve to reduce any tendency of the mount to maintain large amplitude, low frequency vibrations of the type generally due to casing movement, shock, touching, etc.

Thus, the novel transducer mount comprises a pluraiity of open-ended, hollow, tubular members, as shown in FIGURE 2. These hollow tubular members serve to isolate the transducer from the effects of mechanical vibratory feedback by .the use of a moving air column within the tubes to provide highly desirable non-linear damping and non-linear compliance characteristics. In one partinlar embodiment of the invention, which has been used successfully to date, it was found that each tubular member provided a highly effective isolation from mechanical vibratory feedback when made with a .040 inch outer diameter, a .030 inch inner diameter and a length of .100 inch. However, those skilled in the art will readily appreciate that these dimensions are merely illustrative and that the tubular members may be formed with other dimensions in accordance with the invention.

FIGURES 3, 4, and 5 illustrate still further advantageous features of the present invention. FIGURE 3, for example, shows the hollow, tubular members 26 on the sheath 34, such as a band or boot, in their normal, uncompressed condition, prior to being inserted in the cavity 12 of the hearing aid case 14.

It will be appreciated by those skilled in the art that the tubular members 26 may be mounted with their outer peripheral surfaces tangent to or even slightly raised above, the outer surface of the inter-connecting sheath 34. This arrangement has the advantage that the tubular members 26 are not materially deformed upon stretching of the sheath 34, as might occur when the sheath is mounted upon a transducer of different size.

Those skilled in the art will appreciate that the transducer 10 normally vibrates in a direction perpendicular to the plane of the transducer diaphragm, as indicated by the arrow 30, shown in FIGURE 4. The hollow tubular members 26 positioned adjacent the side walls of the casing '14 roll with this motion, and therefore, the only coupling between the side walls of the casingand the transducer is the co-eilicient of rolling friction which is extremely low. Similarly, as shown in FIGURE 5, when the transducer is moved in a horizontal fashion as indicated by the arrow 32, the hollow tubular members 26- between the transducer and the upper and lower walls of the casing 14 roll with such motion and therefore, the only coupling between these casing walls and the transducer is the co-efficient of rolling friction which is extremely low.

It can now be appreciated that the isolation of the transducer within the casing 14 by air-filled tubular members 26 is not destroyed by any stiffness of coupling between the transducer and the side, upper or lower walls of the casing.

In accordance with another feature of this invention, the hollow tubular members 26 may be positioned on a pair of sheaths, either of bands, or boots such as that illustrated in FIGURE 2, which fit over the opposite ends of the transducer 10. In the prior art, one of the problems in transducer mounting resulted from the lack of uniform techniques for this operation which often resulted in unsatisfactory production efliciencies. Thus, skillful operators generally were needed to locate the transducers properly Within the casing recesses and often special buffers had to be added to properly locate and seat the transducer.

In accordance with a feature of this present invention, these prior art disadvantages are eliminated since the airfilled, hollow, tubular members 26 serve to properly locate and seat the transducer within its casing cavity in a uniform and relatively simple manner. It has been found, through the use of the new suspension means, that the transducer and suspension assembly need only to be dropped into the casing cavity and the air tubes serve to automatically and properly locate the assembly within the cavity. This has resulted in a very high efiiciency of assembly with an extremely low number of rejects to provide considerable savings in assembly and repair costs.

While there has been shown and described a specific embodiment of the present invention, it will, of course, be understood that various modifications and alternative constructions may be made Without departing from the true spirit and scope of the invention. Therefore, it is intended by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

1. The improvement of a transducer suspension system for attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a rigid casing having a plurality of walls defining a cavity shaped to receive a transducer in operative position therewithin, a plurality of hollow tubular members disposed around said transducer to space said transducer from the Walls of said cavity, said hollow tubular members having non-linear compliance and non-linear damping characteristics for effective damping of large amplitude and low frequency vibrations arising from casing movement and shock, and sheath means for said hollow tubular members positioned around said transducer between said members and said transducer, said sheath means being formed of relatively inert material having low internal damping characteristics.

2. The improvement of a transducer suspension system for attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a rigid casing having a plurality of walls defining a cavity shaped to receive a transducer in operative position therewithin, a plurality of hollow tubular members disposed around said transducer to space said transducer from the walls of said cavity, there being at least one such hollow tubular member at each transducer wall, said hollow tubular members having nonlinear compliance and non-linear damping characteristics for effective damping of large amplitude and low frequency vibrations arising from casing movement and shock, and sheath means for said hollow tubular members positioned around said transducer between said members and said transducer.

3. The improvement of a transducer suspension system for attentuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a rigid casing having a plurality of walls defining a cavity shaped to receive a transducer in operative position therewithin, and a plurality of hollow tubular members disposed around said transducer to space said transducer from the walls of said cavity, said hollow tubular members being formed of a visco-elastic material having non-linear compliance and non-linear damping characteristics for effective damping of large amplitude and low frequency vibrations arising from casing movement and shock.

4. The improvement of a transducer suspension system for attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a rigid casing having a plurality of walls defining a cavity shaped to receive a transducer in operative position therewithin, a sheath of relatively inert Visco-elastic material having low internal damping characteristics positioned around said transducer in closely adhering relationship and a plurality of hollow, open-ended, visco-elastic members disposed around said sheath to space said transducer from the walls of said cavity, said hollow, open-ended, visco-elastic members having non-linear compliance and non-linear damping characteristics for effective damping of large amplitude and low frequency vibrations arising from casing movement and shock.

5. The improvement of a transducer suspension system in accordance with claim 4, wherein said hollow, openended, visco-elastic members are shaped to enable said transducer suspension system to roll within the casing in response to casing motion for reducing the coupling between the transducer suspension system and the casing walls.

-6. The improvement of transducer suspension means for use in attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a plurality of spaced hollow tubular members disposed around the transducer, said hollow tubular members being formed of relatively inert material to the end that the isolation of the transducer from the casing is provided by the compliance of said hollow tubular members in combination with the damping effects of the moving air column within said tubular members.

7. The improvement of transducer suspension means for use in attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustical transducer comprising a sheath of relatively inert visco-elastic material positioned around said transducer in closely adhering relationship, and a plurality of spaced hollow tubular members disposed around said sheath, said hollow tubular members being formed of relatively inert visco-elastic material and being mounted in tangential relationship to said sheath such that the isolation of the transducer from the casing is provided by the compliance of said hollow tubular members in combination with the damping effects of the moving air column within said tubular members.

8. The improvement of transducer suspension means in accordance with claim 7 wherein said tubular means comprises open-ended cylindrical tubes each having its longitudinal axis parallel to the plane of the adjacent wall of the transducer.

9. The improvement of transducer suspension means for use in attenuating mechanical vibratory transmission from a rigid casing to an electro-acoustic transducer comprising a sheath formed of relatively inert moldable mate rial having low internal damping characteristics and 7 shaped to be positioned in closely fitting relationship around the transducer, and a plurality of hollow, openended, tubular members integrally molded with said sheath and disposed in spaced relationship therearound for enabling the transducer to be isolated from the casing by the compliance of the hollow tubular members in combination with the damping effects of the moving air column Within said tubular members.

10. The improvement of transducer suspension means in accordance with claim 9 wherein said moldable material comprises non-linear damping and non-linear compliance S characteristics effective to reduce the sustenance of large amplitude, low frequency vibrations arising from casing movement and shock.

11. The improvement of transducer suspension means in accordance with claim 9 wherein said tubular members are positioned with their outer peripheral surfaces tan gential to the outer surface of said sheath to minimize distortion of said tubular members upon stretching of said sheath.

No references cited. 

